Process using hydroxylamine-gallic acid composition

ABSTRACT

A hydroxylamine-gallic compound composition comprises a hydroxylamine compound, at least one alcohol amine compound which is miscible with the hydroxylamine compound and a gallic compound. A process for removing photoresist or other polymeric material or a residue from a substrate, such as an integrated circuit semiconductor wafer including titanium metallurgy, in accordance with this invention comprises contacting the substrate with a hydroxylamine compound, an alcohol amine compound which is miscible with the hydroxylamine compound and a gallic compound for a time and at a temperature sufficient to remove the photoresist, other polymeric material or residue from the substrate. Use of a gallic compound in place of catechol in the composition and process reduces attack on titanium metallurgy by, e.g., about three times.

ORIGIN OF THE INVENTION

This application is a division of application Ser. No. 08/628,060, filedApr. 17, 1996, now U.S. Pat. No. 6,187,730, which is acontinuation-in-part of application Serial No. 08/078657, filed Jun. 21,1993, now abandoned, which is in turn a continuation-in-part ofapplication Ser. No. 07/911,102, filed Jul. 9, 1992, now U.S. Pat. No.5,334,332, which was a continuation-in-part of application Ser. No.07/610,044, filed Nov. 5, 1990, now U.S. Pat. No. 5,279,771. Thedisclosures of those applications are hereby incorporated by referencein this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a stripping and cleaningcomposition and process for removal of polymeric materials and organic,organometallic and metal oxide residues from substrates. Moreparticularly, it relates to such a composition and process for removingpolymers, such as photoresist, polyimide, and the like and etchingresidues after plasma etching processes in the fabrication of integratedcircuits and similar processes. Most especially, it relates to such acomposition and process which is effective for the removal of thesematerials while avoiding substantial attack on metal layers employed inintegrated circuits, including titanium layers.

2. Description of the Prior Art

As integrated circuit manufacturing has become more complex and thedimensions of circuit elements fabricated on silicon or othersemiconductor wafers have become smaller, continued improvement intechniques used to remove photoresist or other polymeric materials andresidues formed from such materials has been required. Photoresist orother polymeric materials, such as polyimide, are often subjected to ionimplantation, plasma etching, reactive ion etching or ion milling duringthe fabrication processes to define patterns in the substrate.Additionally, oxygen plasma oxidation is often used for removal ofphotoresist or other polymeric materials after their use during thefabrication process has been completed. Such high energy processestypically result in the hardening of the photoresist and the formationof organometallic and other residues on sidewalls of the structuresbeing formed in the fabrication process.

A variety of metal and other layers are commonly employed in integratedcircuit fabrication, including aluminum, aluminum/silicon/copper,titanium, titanium nitride, titanium/tungsten, tungsten, silicon oxide,polysilicon crystal, and the like. The use of such different layersresults in the formation of different organometallic residues in thehigh energy processes. In addition to being effective for removingphotoresist or other polymeric materials or residues, stripping andcleaning compositions should also not attack the different metallurgiesused in integrated circuit fabrication.

SUMMARY OF THE INVENTION

Hydroxylamine based compositions, as described in the above-referencedpredecessor applications and issued patents, and which are commerciallyavailable from EKC Technology, Inc., the assignee of this application,have been proven as very efficient photoresist and etching residueremoving formulations in the integrated circuit industry. As a result ofa continuous effort to decrease critical dimension size in theintegrated circuit industry, such as in the fabrication of sub-micronsize devices, etching residue removal and substrate compatibility withchemicals employed in wet processing is becoming more and more criticalfor obtaining acceptable yield in very large scale integration (VLSI)and ultra large scale integration (ULSI) processes. The composition ofsuch etching residue is generally made up of the etched substrates,underlying substrate, photoresist and etching gases. The substratecompatibility of the wafers with wet chemicals, such as thehydroxylamine compositions, is highly dependent on the processing of thepolysilicon, multilevel interconnection dielectric layers andmetallization in thin film deposition, etching and post-etch treatmentof the wafers, which are often quite different from one fabricationprocess to another.

In some circumstances, hydroxylamine compositions, such as thosecontaining catechol (1,2-dihydroxybenzene), have produced corrosion oncertain metal substrates, such as those including a titanium metallayer, or those including an aluminum layer at high temperatures, i.e.in excess of 65° C. Titanium has become more widely used insemiconductor manufacturing processes. It is employed both as a barrierlayer to prevent electromigration of certain atoms and as anantireflector layer on top of other metals. Catechol is considered ahazardous material under applicable Federal regulations (SERA TitleIII). In a drive to introduce more effective and less toxic wet chemicalproducts for the semiconductor industry, research has been carried outto find a suitable replacement for catechol in hydroxylaminecompositions.

Accordingly, it is an object of this invention to provide an improvedhydroxylamine based composition and process using such a compositionsuitable for meeting current semiconductor fabrication requirements.

It is another object of the invention to provide such a composition andprocess which is suitable for removing photoresist and other polymericmaterials and residues from wafers and other substrates including one ormore titanium metal layers without substantial attack on such titaniumlayers.

It is a further object of the invention to provide such a compositionand process which contains more healthy and environmentally friendlychemicals.

The attainment of these and related objects may be achieved through useof the hydroxylamine-gallic compound composition and process hereindisclosed. A hydroxylamine-gallic compound composition in accordancewith this invention comprises a hydroxylamine compound, at least onealcohol amine compound which is miscible with the hydroxylamine compoundand a gallic compound. A process for removing photoresist or otherpolymeric material or a residue from a substrate in accordance with thisinvention comprises contacting the substrate with a composition thatcontains a hydroxylamine compound, an alcohol amine compound which ismiscible with the hydroxylamine compound and a gallic compound for atime and at a temperature sufficient to remove the photoresist, otherpolymeric material or residue from the substrate.

In practice, we have found that substitution of a gallic compound inapproximately equivalent amounts for catechol gives a photoresiststripping and cleaning or residue removing composition that attackstitanium at least about three times less than the composition containingcatechol. At the same time, the gallic compound containing compositiongives equivalent performance as a photoresist stripping and cleaning orresidue removing composition.

The attainment of the foregoing and related objects, advantages andfeatures of the invention should be more readily apparent to thoseskilled in the art, after review of the following more detaileddescription of the invention, taken together with the drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are graphs showing comparative results on titanium thicknessmeasurements after treatment by another stripping and cleaning andresidue removing composition compared with a stripping and cleaning andresidue removing composition in accordance with the invention.

FIGS. 5A-14B are scanning electron microscope (SEM) photographs showingcomparative results achieved using the composition and process of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The hydroxylamine suitable for use in the invention has the structuralformula H₂N—OH. Hydroxylamine has properties which, in many ways, liebetween those of hydrazine, H₂N—NH₂, and hydrogen peroxide, HO—OH, asits formula might suggest. Hydroxylamine in its pure form is a colorlessdeliquescent solid having a melting point of 33° C., which explodes onheating and decomposes slowly, evolving nitrous oxide and nitrogen atambient or room temperature. Hydroxylamine is commercially available inan about 50% by weight in water as an aqueous solution from NissinChemical. A proprietary stabilizer is added by Nissin Chemical to thesolution to improve its storage stability. In practice, thiscommercially available form of hydroxylamine is employed in the presentinvention, and the recitation of amounts refer to the commerciallyavailable form. Hydroxylamine is reported by the manufacturer to beincompatible with titanium.

The alcohol amines suitable for use in the present invention aremiscible with the hydroxylamine and are preferably water-soluble.Additionally, the alcohol amines useful in the present inventionpreferably have relatively high boiling points, such as for example, 75°C. or above. Suitable alcohol amines are primary, secondary or tertiaryamines and are preferably monoamines, diamines or triamines, and, mostpreferably, monoamines. The alcohol group of the alcohol aminespreferably has from 1 to 6 carbon atoms, and can be based on a linear,branched or cyclic alcohol.

Preferred alcohol amines suitable for use in the present invention canbe represented by the chemical formula:

R₁R₂—N—CH₂CH₂—O—R₃ wherein R₁ and R₂ can be H, CH₃, CH₃CH₂ or CH₂CH₂OHand R₃ is CH₂CH₂OH.

Examples of suitable alcohol amines include monoethanolamine,diethanolamine, triethanolamine, tertiarybutyldiethanolamine,isopropanolamine, diisopropanolamine, 2-amino-1-propanol,3-amino-1-propanol, isobutanolamine, 2-amino-2-ethoxyethanol(diglycolamine), 2-amino-2-ethoxy-propanol and 1-hydroxy-2-aminobenzene.

The gallic compounds suitable for use in the present invention have thestructural formula:

wherein R is hydrogen, an alkyl group or an aryl group containing from 1to 10 carbon atoms and X is hydrogen, a halogen or an alkyl groupcontaining from 1 to 5 carbon atoms. The preferred gallic compounds aregallic acid, i.e., R and X are hydrogen, or propyl gallate, i.e., R ispropyl and X is hydrogen.

The composition desirably contains at least about 5% by weight ofhydroxylamine, at least about 10% by weight of at least one alcoholamine and from about 2% to about 30% by weight of the gallic compound.The balance of the composition is made up of water, preferably highpurity deionized water, or another suitable polar solvent The solventscan be used singly or as mixtures. The composition preferably includesfrom about 5% to about 80% by weight hydroxylamine, from about 10% toabout 80% by weight of at least one alcohol amine, from about 5% toabout 30% by weight of the gallic compound, with the remaining balancebeing water or other suitable polar solvent.

While Applicant does not intend to be bound by any particular theory ofoperation, it is believed that the alcohol amine reacts in situ with thegallic compound in the composition to form either an amide or ammoniumphenolate salt.

Suitable examples of polar solvents for the composition, in addition towater, include dimethyl sulfoxide, ethylene glycol, ethylene glycolalkyl ether, diethylene glycol alkyl ether, triethylene glycol alkylether, propylene glycol, propylene glycol alkyl ether, dimethylsulfoxide, N-substituted pyrrolidone, ethylene diamine andethylenetriamine. Additional polar solvents as known in the art can alsobe used in the composition of the present invention.

The stripping and cleaning compositions of the present composition areeffective in removing a wide range of positive photoresists but areparticularly useful in removing photoresists commonly consisting of anorth-naphthoquinone diazide sulfonic acid ester or amide sensitizer withnovolak-type binders or resins. Examples of commercially availablephotoresist compositions which the stripping and cleaning compositionsof the present invention effectively remove from a substrate includeK.T.I. photoresists 820, 825; Philip A. Hunt Chemical Corp. Waycoat HPR104, HPR 106, HPR 204 and HPR 206 photoresists; Shipley Company, Inc.photoresists of the AZ-1300 series, AZ-1400 series and AZ-2400 series;and Tokyo Ohka Kogyo Co., Ltd. photoresist OFPR-800.

Further, the stripping and cleaning compositions of the presentinvention are effective in removing polyimide coatings from substrateseven when the polyimide coatings have been subjected to a hightemperature cure, including a cure performed at a temperature as high asabout 400° C. Examples of commercially available polyimide compositionswhich the stripping and cleaning compositions of the present inventioneffectively remove from a substrate includes Ciba Geigy Proimide 293,Asahi G-6246-S, and DuPont PI2545 and PI2555.

Examples of substrates from which the stripping and cleaningcompositions of the present invention remove photoresists withoutattaching the substrates themselves include metal substrates such asaluminum, titanium, tungsten, titanium/tungsten/aluminum/silicon/copper,and substrates such as silicon oxide, silicon nitride, andgallium/arsenide; and plastic substrates such as polycarbonate.

The stripping and cleaning compositions of the present invention arealso effective in removing organometallic and metal oxide residuegenerated on the substrate of the etching equipment utilized. Examplesof commercially available etching equipment include that available fromLam Research, Tegal, Electrotech, Applied Materials, Tokyo Electron,Hitachi and the like.

The method of removing a resist or other material from a substrate usingthe stripping and cleaning compositions of the present inventioninvolves contacting a substrate having a resist thereon with a strippingand cleaning composition of the present invention for a time and at atemperature sufficient to remove the resist. The time and temperatureare determined based on the particular material being removed from asubstrate. Generally, the temperature is in the range of from aboutambient or room temperature to about 120° C. and the contact time isfrom about 2 to 60 minutes. Additionally the temperture may be in therange of from about room temperature to 100° Celsius.

The method of stripping and cleaning a substrate using the stripping andcleaning compositions of the present invention involves contacting asubstrate having organometallic and metal oxide residue thereon with astripping and cleaning composition of the present invention for a timeand at a temperature sufficient to remove the residue. The substrate isgenerally immersed in the stripping and cleaning composition. The timeand temperature are determined based on the particular material beingremoved from a substrate. Generally, the temperature is in the range offrom about ambient or room temperature to about 120° C. and the contacttime is from about 2 to 60 minutes.

In either case, the substrate may then be rinsed in a polar solvent,such as isopropyl alcohol, followed by a deionized water rinse. Thesubstrate is then mechanically dried, such as with a spin drier, ornitrogen blow dried.

The following represent non-limiting examples and describe the inventionfurther.

Examples of stripping and cleaning compositions according to the presentinvention suitable for removing a resist from a substrate or forremoving resist or other organic residues from a substrate are set forthin Table I below. Compositions A and G are comparative compositionsemployed to give a frame of reference for the results obtained with thegallic compound containing compositions. Composition F is a prior artcomposition used for photoresist and residue removal in one of theexamples below.

TABLE 1 Stripping and Commercial Cleaning Hydroxylamine* Alcohol amineAdditive Additional Composition Wt. % Wt. % Wt. % Solvent Wt. % A 35%60% Monoethanol- 5% Catechol amine B 35% 60% Monoethanol- 5% Gallicamine acid C 30% 60% Monoethanol 10% Gallic amine acid D 30% 60%Isopropanol- 10% Gallic amine acid E 45% 45% Diglycolamine 10% Gallicacid F 0 50% Diglycolamine 50% N-Ethyl hydroxyl-2- pyrolidone G 35% 60%Diglycolamine 5% Catechol H 30% 60% Diglycolamine 10% Propyl gallate I30% 55% Diglycolamine 10% Gallic 5% acid Water J 30% 55% Diglycolamine10% Gallic 5% Dimethyl- acid sulfoxide K 30% 30% Diglycolamine 10%Gallic 30% Monoethanol- amine L 35% 60% Isopropanol- 5% Gallic amineacid M 20% 55% Monoethanol- 15% Gallic 10% amine acid Water *Includesapproximately 50% by weight water.

EXAMPLE 1

This example shows that substitution of gallic acid for catechol in ahydroxylamine stripping and cleaning composition makes the stripping andcleaning composition much less corrosive to titanium metallurgy onsemiconductor wafers than the catechol containing stripping and cleaningcomposition. The change in dimension of a metallurgy film used insemiconductor manufacturing can be determined by measuring the change ofits sheet resistance using the following equation:

Sheet Resistance=Resistivity/Film Thickness.

Experiments were carried out with wafers having a sputtered titaniumfilm of nominal thickness of 3500-4000 Angstroms, as determined bymeasuring the sheet resistance using a Prometrix Four Point Probe. Thewafer samples were immersed in compositions A, B, C, D, G and I listedin Table 1 for 30, 60 and 120 minutes at 75° C. An higher measured sheetresistance results from greater attack of a titanium film.

FIGS. 1-4 are graphs of the resulting measurements in the form of thepercentage thickness remaining plotted against time. FIG. 1 is acomparison of compositions A and B (catechol vs. gallic acid in amonoethanolamine system). FIG. 2 is a comparison of compositions G and I(catechol vs. gallic acid in a diglycolamine system). FIG. 3 is acomparison of compositions B and C, showing the effect of gallic acidconcentration in a monoethanolamine system. FIG. 4 is a comparison ofcompositions C and D (gallic acid in a monoethanolamine system vs.gallic acid in an isopropanolamine system).

FIG. 1 clearly shows the reduction in titanium attack obtained withstripping and cleaning composition B, containing gallic acid, comparedagainst prior art stripping and cleaning composition A, containingcatechol in otherwise identical hydroxylamine stripping and cleaningsolutions.

EXAMPLE 2

Composition M was used to show that the present invention also removesmobile ion contamination from the wafer surface. Wafer samples wereprepared for mobile ion contamination evaluation in the followingmanner. A metal film consisting of TiN/AlSi/TiN/Ti was sputter depositedon boron tetraethylorthosilicate (BTEOS) wafers. The wafers were thenpatterned with photoresist and the metal film etched in a plasma etchsystem. The photoresist was removed by oxygen plasma ashing.Contamination on the BTEOS surface is measured by an SIMS probe beforeand after processing in composition M for 30 minutes at 75° C. Allsamples were rinsed in deionized water for five cycles in a Sprayrinser. The samples were then dried with a nitrogen gun. Table 2 showsthe results obtained with and without the processing with composition M.

TABLE 2 Na Content in Na content on BTEOS solution (ppm) surfaceatoms/cm² Unprocessed wafer — 4.16 × 10¹¹ Composition M 9.09 1.18 × 10¹¹

This result shows that composition M can remove sodium from the wafersurface.

EXAMPLE 3

A via opening with a size of 1.2 micron in a silicon oxide dielectriclayer was etched through a photoresist patterned opening using astandard silicon oxide plasma etching process. The photoresist wasremoved by oxygen plasma ashing. FIG. 5A is a micrograph of a scanningelectron microscope (SEM) image, showing that heavy organometallic etchresidue remained on the substrate surface, particularly around the viaopening. The substrate was then processed in composition B for 30minutes at 70° C. FIG. 5B, the resulting SEM photograph, shows thatcomposition B removed all the organometallic residue.

EXAMPLE 4

Via openings with a size of 0.6 micron in a silicon oxide dielectriclayer overlying a metal film of TiN/Al—Si—Cu were etched throughphotoresist patterned openings using a standard silicon oxide plasmaetch process. The photoresist was removed using oxygen plasma ashing.FIGS. 6A and 6B, SEM micrographs, showed that heavy etch residueremained on the via openings. The micrograph of FIG. 6C showed thatcomposition E completely removed all the residue after processing incomposition E for 30 minutes at 70° C. Composition F, a commerciallyavailable photoresist stripper containing N-ethylhydroxy-2-pyrrolidone,partially removed the etching residue after processing for 30 minutes at120° C., as shown in FIG. 6D.

EXAMPLE 5

This example shows operability of a stripping and cleaning compositionin which propyl gallate is substituted for catechol. Composition H wasused on plasma oxide etched via wafers. Oxygen plasma ashing usuallyfollows the plasma oxide etching process step. In this experiment, thephotoresist used as a mask for the via etch was not removed by theoxygen plasma ashing step on some of the wafers in order to demonstratethat the stripping and cleaning composition can also remove plasma etchtreated photoresist. FIG. 7A shows the via wafer with the photoresistlayer after via etch. FIG. 7B shows organometallic and oxide residueremaining on the wafer surface after oxygen plasma ashing. FIGS. 7C and7D show that composition H effectively removed photoresist afterexposure to a plasma oxide etching environment and removedorganometallic and oxide residue remaining after oxygen plasma ashingwithout difficulty after processing at 65° C. for 30 minutes.

EXAMPLE 6

This example shows differential attack of composition G, containingcatechol, and composition I, containing gallic acid. A sandwich metalthin film substrate of TiN/AlSi/Ti/TiN/Ti metallurgy was patterned andetched in a plasma metal etcher. FIG. 8A shows that there isorganometallic residue left on the metal line surface after photoresistremoval by oxygen plasma ashing. The titanium barrier layer (Ti/TiN/Ti)was undercut after the wafer was exposed to composition G at 75° C. for30 minutes, as shown in FIG. 8B. Under the same process conditions,stripper composition I, containing gallic acid, did not attack thebarrier layer, as shown in FIG. 8C.

EXAMPLE 7

This example further illustrates the reduction of attack on a titaniumbarrier metal film by a stripping and cleaning composition containinggallic acid. The test was carried out on a plasma metal etched waferwith a W/Ti metallurgy. Photoresist was removed by oxygen plasma ashing.The wafer was immersed into the stripping and cleaning solution at 75°C. for 30 minutes. The titanium barrier layer was severely laterallyattacked by composition G, containing catechol, as shown in FIG. 9A.Stripping and cleaning composition I, containing gallic acid, did nothave any impact on the titanium film, as shown in FIG. 9B.

EXAMPLE 8

This example shows that additional polar solvent can be added to thehydroxylaminelgallic acid stripping and cleaning composition withoutimpairing its performance. FIGS. 10A and 10B show the result of plasmaetched metal and via wafers which have been processed in composition Jfor 30 minutes at 75° C. Composition J removed all the etching residueswithout attacking the titanium barrier metal layer.

EXAMPLE 9

This example demonstrates that composition K, a hydroxylamine/ gallicacid stripping and cleaning composition using isopropanolamine as analcohol amine, removed all etching residues without attacking thetitanium barrier metal layer. FIGS. 11A, 11B and 11C show the result ofplasma etched metal and via wafers which have been processed incomposition K for 30 minutes at 75° C.

EXAMPLE 10

This example shows that a hydroxylamine stripping and cleaningcomposition containing gallic acid is able to remove post etchphotoresist residues from a polysilicon substrate. Silicon wafers havingan etched polysilicon layer with a thickness of about 400 nm wereimmersed in composition I at 95° C. for 30, 45 and 60 minutes. Thewafers were then dried by a dry nitrogen gun. The wafers were thenexamined by an Hitachi S-4500 FE Scanning Electron Microscope (SEM) toevaluate the capability of composition B to remove etching residues.

SEM photographs of the unprocessed and processed wafers are shown inFIGS. 12A, 12B, 12C, 12D and 12E. Most of the residues are on thesidewalls of the polysilicon lines, as shown in FIGS. 12A and 12B. Afterimmersion in composition I for 30 and 45 minutes, most of the residuesare removed, as shown in FIGS. 12C and 12D. The residues are completelyremoved after immersion in composition I for 60 minutes, as shown inFIG. 12E, which is an acceptable process condition for waferfabrication.

EXAMPLE 11

This example shows that gallic acid performs equally well with a mixtureof alcohol amines. Composition K is a solution containingmonoethanolamine and diglycolamine. FIGS. 13A and 13B show itseffectiveness in removing residue without attacking a titanium barriermetal layer in metal and via etch wafers after treatment withcomposition K at 75° C. for 30 minutes and 60 minutes.

EXAMPLE 12

Composition L, in which the alcohol amine is isopropanolamine,effectively removed all etching residue after metal and via etch withoutattacking a Ti barrier metal layer when used for processing at 75° C.for 60 minutes, as shown in FIG. 14A. FIG. 14B demonstrates itseffectiveness in cleaning via etch residues from a via opening.

In summary, the above examples show that compositions B-E and H-L havethe capability to remove photoresist and etching residues on variouswafers, such as metal, via and polysilicon wafers, without adverseeffects on the substrates. These compositions exhibit superiorperformance in substrate compatibility, especially with Ti and Al metalfilms at high temperature, in comparison to compositions A, F and G.Compositions B-E and H-L contain no substances which are subject to thereporting requirements of Section 313 of the Emergency Planning andCommunity Right-To-Know Act of 1986 and of 40 CFR 372, unlikecompositions A and G.

It should now be readily apparent to those skilled in the art that anovel composition and process capable of achieving the stated objects ofthe invention has been provided. The improved hydroxylamine basedcomposition and process using such a composition of this invention issuitable for meeting current semiconductor fabrication requirements. Thecomposition and process is suitable for removing photoresist and otherpolymeric materials and residues from wafers and other substratesincluding one or more titanium metal layers without substantial attackon such titanium layers. The composition and process does not contain oruse any material subject to reporting requirements.

It should further be apparent to those skilled in the art that variouschanges in form and details of the invention as shown and described maybe made. It is intended that such changes be included within the spiritand scope of the claims appended hereto.

What is claimed is:
 1. A process for removing photoresist residue orother polymeric material from a substrate which comprises contacting thesubstrate with a cleaning composition comprising about 5% to 50% byweight of hydroxylamine, about 10% to 80% by weight of at least one analcohol amine compound which is miscible with the hydroxylamine, fromabout 5% to about 30% by weight of gallic acid and the balance beingwater, for a time and at a temperature sufficient to remove thephotoresist, residue or other polymeric material from the substrate. 2.The process of claim 1 in which the time is from about 2 minutes toabout 60 minutes and the temperature is from room temperature to about100° Centigrade.
 3. The process of claim 1 in which said at least onealcohol amine is a monoamine, diamine or triamine with an alcohol grouphaving from 1 to 5 carbon atoms.
 4. The process of claim 3 in which saidat least one alcohol amine has the formula: R₁R₂—N—CH₂CH₂—O—R₃ whereinR₁ and R₂ are, independently in each case, H, CH₃, CH₃CH₂ or CH₂CH₂OHand R₃ is CH₂CH₂OH.
 5. The process of claim 1 in which said at least onealcohol amine comprises at least two alcohol amines.
 6. The process ofclaim 5 in which one of said at least two alcohol amines ismonoethanolamine.